Solid electrolytic capacitor and method for manufacturing the same

Abstract

A solid electrolytic capacitor includes an anode foil, a solid electrolyte provided on the anode foil and made of conductive polymer, and a cathode foil provided on the solid electrolyte and facing the anode foil across the solid electrolyte. The anode foil includes an anode base made of aluminum, a rough surface layer made of aluminum and provided on a surface of the anode base, and a dielectric oxide layer provided on the rough surface layer and contacting the solid electrolyte. The cathode foil includes a cathode base made of aluminum, and a nickel layer provided on a surface of the cathode base and contacting the solid electrolyte. The nickel layer faces the dielectric oxide layer of the anode foil across the solid electrolyte. The nickel layer is made of nickel and nickel oxide. This solid electrolytic capacitor has a large capacitance and a low equivalent series resistance while being inexpensive and highly reliable.

The invention claimed is: 
     
       1. A solid electrolytic capacitor comprising:
 an anode foil; 
 an solid electrolyte provided on the anode foil and made of conductive polymer; and 
 a cathode foil provided on the solid electrolyte and facing the anode foil across the solid electrolyte, wherein 
 the anode foil includes
 an anode base made of aluminum, 
 a first rough surface layer made of aluminum and provided on a first surface of the anode base, and 
 a first dielectric oxide layer provided on the first rough surface layer and contacting the solid electrolyte, 
 
 the cathode foil includes
 a cathode base made of aluminum, and 
 a nickel layer provided on a surface of the cathode base and contacting the solid electrolyte, the nickel layer facing the first dielectric oxide layer of the anode foil across the solid electrolyte, the nickel layer being made of nickel and nickel oxide, 
 
 the surface of the cathode foil is roughened and has a plurality of pores therein, and 
 the nickel layer is not formed inside the plurality of pores in the surface of the cathode foil. 
 
     
     
       2. The solid electrolytic capacitor according to  claim 1 , wherein a mode of diameters of pores in the first rough surface layer of the anode foil ranges from 0.02 to 0.10 μm. 
     
     
       3. The solid electrolytic capacitor according to  claim 2 , further comprising:
 a second rough surface layer provided on a second surface of the anode base opposite to the first surface of the anode base, the second rough surface layer being made of aluminum; and 
 a second dielectric oxide layer provided on the second rough surface layer, wherein 
 a mode of diameters of pores in the second rough surface layer ranges from 0.02 to 0.1 μm, and 
 a total of thicknesses of the first and the second rough surface layers ranges from 20 to 80 μm. 
 
     
     
       4. The solid electrolytic capacitor according to  claim 3 , wherein the second rough surface layer includes a plurality of tree structures extend from the second surface of the anode base, each of the plurality of tree structures comprising a plurality of fine particles of aluminum, link to one after another, and branch into a plurality of twigs. 
     
     
       5. The solid electrolytic capacitor according to  claim 1 , further comprising:
 a second rough surface layer provided on a second surface of the anode base opposite to the first surface of the anode base, the second rough surface layer being made of aluminum; and 
 a second dielectric oxide layer provided on the second rough surface layer. 
 
     
     
       6. The solid electrolytic capacitor according to  claim 5 , wherein the second rough surface layer includes a plurality of tree structures extend from the second surface of the anode base, each of the plurality of tree structures comprising a plurality of fine particles of aluminum, link to one after another, and branch into a plurality of twigs. 
     
     
       7. The solid electrolytic capacitor according to  claim 1 , wherein the first rough surface layer includes a plurality of tree structures extend from the first surface of the anode base, each of the plurality of tree structures comprising a plurality of fine particles of aluminum, link to one after another, and branch into a plurality of twigs. 
     
     
       8. The solid electrolytic capacitor according to  claim 1 , further comprising an insulating separator provided between the anode foil and the cathode foil, wherein the solid electrolyte is impregnated into the separator. 
     
     
       9. The solid electrolytic capacitor according to  claim 8 , wherein the separator is made of electrolytic paper mainly made of cellulose fiber. 
     
     
       10. The solid electrolytic capacitor according to  claim 9 , wherein the electrolytic paper of the separator is carbonized. 
     
     
       11. The solid electrolytic capacitor according to  claim 8 , wherein the separator is made mainly of chemical fiber. 
     
     
       12. The solid electrolytic capacitor according to  claim 8 , wherein the anode foil, the cathode foil, the solid electrolyte, and the separator are rolled together to provide a capacitor element, said solid electrolytic capacitor further comprising:
 a case having an opening and accommodating the capacitor element; and 
 a sealing member for sealing the opening of the case. 
 
     
     
       13. The solid electrolytic capacitor according to  claim 8 , wherein the anode foil, the cathode foil, the solid electrolyte, and the separator are stacked together. 
     
     
       14. A method for manufacturing a solid electrolytic capacitor, comprising:
 providing a rough surface layer made of aluminum on a surface of an anode base made of aluminum; 
 providing a dielectric oxide layer on the rough surface layer; 
 forming a nickel layer made of nickel and nickel oxide on a surface of a cathode base made of aluminum by evaporation; and 
 providing a solid electrolyte between the dielectric oxide layer and the nickel layer such that the solid electrolyte contacts the dielectric oxide layer and the nickel layer, wherein 
 the surface of the cathode base is roughened and has a plurality of pores therein, and 
 the nickel layer is not formed inside the plurality of pores in the surface of the cathode base. 
 
     
     
       15. A solid electrolytic capacitor comprising:
 an anode foil; 
 an solid electrolyte provided on the anode foil and made of conductive polymer; and 
 a cathode foil provided on the solid electrolyte and facing the anode foil across the solid electrolyte, wherein 
 the anode foil includes:
 an anode base made of aluminum; 
 a rough surface layer made of aluminum and provided on a surface of the anode base; and 
 a dielectric oxide layer provided on the rough surface layer and contacting the solid electrolyte, 
 
 the cathode foil includes:
 a cathode base made of aluminum; and 
 a nickel layer provided on a surface of the cathode base and contacting the solid electrolyte, the nickel layer facing the dielectric oxide layer of the anode foil across the solid electrolyte, the nickel layer being made of nickel and nickel oxide, and 
 
 the rough surface layer includes a plurality of tree structures extend from the surface of the anode base, each of the plurality of tree structures comprising a plurality of fine particles of aluminum, link to one after another, and branch into a plurality of twigs. 
 
     
     
       16. A method for manufacturing a solid electrolytic capacitor, comprising:
 providing a rough surface layer made of aluminum on a surface of an anode base made of aluminum; 
 providing a dielectric oxide layer on the rough surface layer; 
 forming a nickel layer made of nickel and nickel oxide on a surface of a cathode base made of aluminum by evaporation; and 
 providing a solid electrolyte between the dielectric oxide layer and the nickel layer such that the solid electrolyte contacts the dielectric oxide layer and the nickel layer, wherein 
 the rough surface layer includes a plurality of tree structures extend from the surface of the anode base, each of the plurality of tree structures comprising a plurality of fine particles of aluminum, link to one after another, and branch into a plurality of twigs.